1. Field of the Invention
The present invention relates to a method and an apparatus for protecting, from corrosion, stainless steel components of an exhaust gas desulfurization apparatus in an exhaust gas treatment system having the exhaust gas desulfurizing apparatus for remove at least sulfur dioxide gas for exhaust gas generated when fossil fuel is burnt by bringing the exhaust gas into contact with an absorbing solution.
2. Description of the Related Art
In general, an exhaust gas desulfurization apparatus operates in an extremely severe corrosive environment. Since exhaust gas from a boiler or the like, to which the exhaust gas desulfurization apparatus is applied, and industrial water used for the absorbing solution in the exhaust gas desulfurization apparatus generally contain chlorine ions (Cl.sup.-), normal stainless steel (for example, SUS304) suffers from pitting corrosion and crevice corrosion if it is simply employed in components of the apparatus which comes to contact with the exhaust gas and the like. Accordingly, carbon steel having a rubber lining or costly and high quality material, such as hastelloy-C, has been employed for the components of the exhaust gas desulfurization apparatus. For cost reduction and ease of maintenance and manufacture, however, a technique which uses the normal is at the same time stainless steel and capable of preventing corrosion has been required in order to reduce cost, easily manufacture the apparatus and easily perform a maintenance operation.
Accordingly, the applicant of the present invention has suggested, in Japanese Patent Provisional Publication No. 223188/1988 (63-223188), a corrosion preventive method accomplished on the basis of a knowledge that sulfate ions (SO.sub.4.sup.2-) are capable of preventing corrosion caused by chlorine ions (Cl.sup.-) by adjusting the ion balance of these ions with addition of sulfate ions.
However, in the corrosion preventive method disclosed in the above publication, a sulfate ion source such as sodium sulfate (Na.sub.2 SO.sub.4) or ammonium sulfate ((NH.sub.4).sub.2 SO.sub.4) is supplied to the line of the exhaust gas desulfurization apparatus and thereby sulfate ions are added, but there is no contrivance about the origin of the sulfate ion source. Therefore, it is required to purchase ammonia sulfate or the like, and a system such as a silo for storing ammonia sulfate or the like is required. Thus, there arises a problem in that costs of building the system and costs for the operation increase.